This project will investigate immunoregulation of the cell-mediated immune response of contact hypersensitivity to 1-fluoro-2,4-dinitrobenzene (DNFB). We will investigate the mechanisms, genetic restrictions, cell-cell interactions, targets of suppression, and roles in maintenance of immune tolerance by first-order (Ts-1) and second-order (Ts-2) suppressor T cells induced by the intravenous injection of DNP-modified syngeneic lymphoid cells (DNP-LC). Cellular interactions involved in efferent suppression of effector DNFB-immune T cells mediated by both suppressor T cells and suppressor T cell auxiliary cells (Ts-aux) will be investigated. Finally, cellular interactions and targets of afferent-acting suppressor T cells induced by both the reactive hapten dinitrobenzene sulfonic acid and the intravenous injection of DNP-modified allogeneic cells will be examined.